The overall objective of this proposed research is to establish the mechanism responsible for the regulation of leucine oxidation by mammalian cells. Studies will be conducted with various intact tissue preparations, isolated liver mitochondria, and the alpha-ketoisocaproate dehydrogenase complex isolated from liver tissue. The specific aims include: (a) to establish the step of the pathway of leucine oxidation in liver which is stimulated by dichloroacetate; (b) to determine whether dichloroacetate is effective in stimulating leucine oxidation in extrahepatic tissues, and if so, the step involved in the stimulation; (c) to establish whether the alpha-ketoisocaproate dehydrogenase complex of liver and other tissues is 'interconvertible' by a phosphorylation-dephosphorylation mechanism; and (d) to determine whether dichloroacetate has any effect upon leucine catabolism in vivo and upon blood plasma concentrations of this amino acid in various physiological and pathological states. The experimental observation of the principal investigator which provides the basis for this proposal is that dichloroacetate causes a striking increase in the oxidation of (C-1 14) leucine to CO2 14 by isolated liver cells. It is proposed that the alpha-ketoisocaproate dehydrogenase complex may be the enzyme responsive to dichloroacetate and thus may be an 'interconvertible' enzyme of considerable importance in the regulation of leucine catabolism.